The present invention relates to a system, apparatus, and method for more uniformly heating objects in a Rapid Thermal Processing (RTP) system. More specifically, the present invention discloses a convenient, inexpensive way to rotate semiconductor wafers treated in such system.
The major problem faced by the field of RTP has been the uniformity of heating of the semiconductor wafers treated in the RTP systems. RTP systems generally have a chamber with at least one wall transparent to radiation from sources of radiation such as lamps. The object to be processed is placed in the chamber and irradiated with radiation from the radiation source so that the object is heated. The chamber with the transparent wall is not strictly necessary in the system, provided that the system controls the atmosphere in which the object is placed during processing. The lamps could then be placed in proximity to the object without the intervening window. Much progress has been made in using batteries of lamps with individual control of each lamp to increase uniformity of the illuminating radiation. However, the uniformity of the resulting material is not sufficient for present and future demands from the industry.
One way to increase the uniformity of result in such systems is to rotate the substrate under the lamps. Many prior art systems have been published to effect this rotation. However, these many systems generally used only one bank of lamps on one side of the semiconductor wafer. The other side of the wafer could then be used for various shafts which penetrated through the chamber walls to mechanically rotate the wafer with respect to the lamps. The prior art is deficient in that the systems are expensive and difficult to seal. The prior art systems also allow contaminants scrubbed from the relatively moving parts to contaminate the chamber. The prior art systems can not be used with banks of lights on either side of the wafer since the shaft, the rotating base holding the wafer, and the fittings necessary to allow the shaft to rotate with respect to the chamber block or otherwise interfere with light from the bank on the same side of the wafer as the shaft, and the resulting light impinging on the wafer is no longer uniform.
Reactors based on the RTP principle often have the entire cross section of one end of the reactor chamber open during the wafer handling process. This construction has been established because the various wafer holders, guard rings, and gas distribution plates, which have significantly greater dimensions and may be thicker than the wafers, must also be introduced into the chamber and must be easily and quickly changed when the process is changed or when different wafer sizes, for example, are used. The reaction chamber dimensions are designed with these ancillary pieces in mind. US Patent 5,580,830 teaches the importance of the gas flow and the use of an aperture in the door to regulate gas flow and control impurities in the process chamber.
The importance of measuring the temperature of the wafer using a pyrometer of very broad spectral response is taught in U.S. Pat. No. 5,628, 564.
A method and apparatus for improved temperature control is taught in U.S. Pat. No. 5,841,110.
The wafer to be heated in a conventional RTP system typically rests on a plurality of quartz pins which hold the wafer accurately parallel to the reflector walls of the system. Prior art systems have rested the wafer on an instrumented susceptor, typically a uniform silicon wafer. Patent application Ser. No. 08/537,409, now U.S. Pat. No. 5,841,110 teaches the importance susceptor plates separated from the wafer.
Rapid thermal processing of III-IV semiconductors has not been as successful as RTP of silicon. One reason for this is that the surface has a relatively high vapor pressure of, for example, arsenic (As) in the case of gallium arsenide (GaAs). The surface region becomes depleted of As, and the material quality suffers. Patent application Ser. No. 08/631,265, now U.S. Pat. No. 5,837,555, supplies a method and apparatus for overcoming this problem.
A method of raising the emissivity of a lightly doped, relatively low temperature wafer by locally heating the wafer with a pulse of light is disclosed in application Ser. No. 08/632,364, now U.S. Pat. No. 5,727,017.
An inflatable seal for an RTP system is disclosed in copending allowed application Ser. No. 08/895,655, filed Jul. 17, 1997, by Aschner et al.
A method, apparatus, and system for RTP an object is disclosed in copending application Ser. No. 08/953,590, filed Oct. 17, 1997, by Lerch et al.
A method of RTP of a substrate where a small amount of a reactive gas is used to control the etching of oxides or semiconductor is disclosed in copending application Ser. No. 08/886,215, by Nenyei et al, filed Jul. 1, 1997.
A method of RTP of a substrate where evaporation of the silicon is controlled is disclosed in copending application Ser. No. 09/015,441, by Marcus et al. filed Jan. 29, 1998.
Methods of rotating the wafer in an RTP system are disclosed in applications Ser. Nos. 08/960,150 and 08/977,019 by Blersch et al. and Aschner et al. filed on Oct. 29. 1997 and Nov. 24, 1997 respectively.
The above identified patents and applications are assigned to the assignee of the present invention and are hereby incorporated herein by reference.
According to this invention, the object to be processed in an RTP system is placed on a rotating susceptor which is protected from warping due to uneven heating of the susceptor from radiation from the hot object.